In ink jet printing, of both the continuous and drop-on-demand approaches, it is necessary to have orifice plate devices that define relatively precise drop ejection passages to form drops of the desired size and direction. The orifice plate devices often comprise a plurality of drop ejection orifices that must be located in a precise interrelation. The orifice plates should be durable, e.g. resistant to chemical reaction with the ink and to wear.
The currently most popular way to accomplish the above objectives is to electroform the orifice plate devices, e.g. by electroplating. U.S. Pat. No. 4,184,925 discloses a highly desirable method to effect such electroforming. In the '925 patent method, cylindrical photoresist pegs are photofabricated on portions of the surface of an electrically conductive metal mandrel. The pegs have a diameter slightly larger than the desired orifice diameter and are inter located at the desired orifice spacings. The peg bearing mandrel is then placed in a conventional electroplating system which is activated so that nickel is deposited onto the conductive mandrel surface, but not upon the dielectric photoresist peg tops. Plating is continued until the thickness of the formed layer reaches the tops of the pegs and then slightly beyond to cause the formed layer to grow over the periphery of the peg tops to an extent that achieves the precise orifice diameter that is wanted.
At this stage the orifice plate can be removed from the mandrel, or its thickness can be increased by forming additional photoresist structures over the formed orifices and electroplating additional material. U.S. Pat. Nos. 4,246,076 and 4,374,707 describe similar electroplating procedures using different photoresist topography to achieve various desired orifice cross sections. U.S. Pat. No. 4,528,577 discloses that such photoresist topography can be used to electroform elements defining ink baffles as well as the orifices.
While the above described electroforming methods have been successfully used for producing commercial devices for some time, there remain problems with the methods. First, the photoresist topography structures (e.g. pegs) are normally usable only for the formation of a single orifice plate so that mandrels must be reimaged with the desired topography as a part of each fabrication sequence. Also, the photoresist portions of the mandrel vary slightly in geometry during each reimage, causing orifices of less than uniform dimension. Further, the photoresist pegs are sometimes defective. For example, small particles from the air sometimes adhere to the photoresist and because of the microscopic size of the pegs. This can cause lower yields for the fabrication process.